Plotinos: Complete Works, v. 1 In Chronological Order,...

(Our answer to the above objection is this:) To begin with, not every residence is necessarily a mass, unless it have already received extension. The soul, which possesses all things, contains them all simultaneously. If it possessed extension, it would possess all things in extension. Consequently matter receives all it contains in extension, because it is capable thereof. Likewise in animals and plants there is a correspondence between the growth and diminution of their magnitude, with that of their quality. It would be wrong to claim that magnitude is necessary to matter because, in sense-objects, there exists a previous magnitude, on which is exerted the action of the forming principle; for the matter of these objects is not pure matter, but individual matter (as said Aristotle).302 Matter pure and simple must receive its extension from some other principle. Therefore the residence of form could not be a mass; for in receiving extension, it would also receive the other qualities. Matter therefore, is the image of extension, because as it is primary matter, it possesses the ability to become extended. People often imagine matter as empty extension; consequently several philosophers have claimed that matter is identical with emptiness. I repeat: matter is the image of extension because the soul, when considering matter, is unable to determine anything, spreads into indetermination, without being able to circumscribe or mark anything; otherwise, matter would determine something.

This substrate could not properly be called big or little; it is simultaneously big and little (as said Aristotle).303 It is simultaneously extended and non-extended, because it is the matter of extension. If it were enlarged or made smaller, it would somehow move in extension. Its indetermination is an extension which consists in being the very residence of extension, but really in being only imaginary extension, as has been explained above. Other beings, that have no extension, but which are forms, are each of them determinate, and consequently imply no other idea of extension. On the contrary, matter, being indeterminate, and incapable of remaining within itself, being moved to receive all forms everywhere, ever being docile, by this very docility, and by the generation (to which it adapts itself), becomes manifold. It is in this way its nature seems to be extension.